為什么我的UILongPressGestureRecognizer無法正常工作？

Question

我有以下代碼，我的長按沒有按應有的方式工作。 有人能弄清楚為什么它不起作用嗎？

override func viewDidLoad() {
    super.viewDidLoad()
    // Do any additional setup after loading the view, typically from a nib.

    let longPressRecognizer = UILongPressGestureRecognizer(target: self, action: "myButton:")
    longPressRecognizer.minimumPressDuration = 0.5
    myButton.addGestureRecognizer(longPressRecognizer)
}

@IBOutlet weak var myButton: UIButton!

@IBAction func myButton(longPress: UILongPressGestureRecognizer) {

    if longPress.state != .Began {

        presentAlertController()

        return
    }
}

當我按住按鈕時會出現此錯誤

2016-01-09 00:41:28.785 longPressTest[1870:551106] Warning: Attempt to present <UIAlertController: 0x144d6a500>  on <longPressTest.ViewController: 0x144e3a450> which is already presenting <UIAlertController: 0x144e59d80>
2016-01-09 00:41:28.903 longPressTest[1870:551106] Attempting to load the view of a view controller while it is deallocating is not allowed and may result in undefined behavior (<UIAlertController: 0x144d6a500>)
2016-01-09 00:41:28.905 longPressTest[1870:551106] Warning: Attempt to present <UIAlertController: 0x144e54bb0>  on <longPressTest.ViewController: 0x144e3a450> which is already presenting <UIAlertController: 0x144e59d80>
Cancel 

Answer 1

長按手勢是連續手勢。 這意味着當識別myButton(_:)檢測到state == .Began的長按開始（0.5秒后）時，識別器將調用您的函數（ myButton(_:) ）。開始，並在state == .Changed的屏幕上移動觸摸時反復進行state == .Changed ，並且當手勢以state == .Ended結束時再次state == .Ended 。 你試圖呈現在每個警報.Changed呼叫並在.Ended呼叫，而當你試圖呈現一個已經被提出警告你的錯誤。

如果要在0.5秒后立即顯示警報，請在狀態為.Began時執行此警報，而不是在狀態為.Began 以外的任何狀態時執行此警報。

@IBAction func myButton(longPress: UILongPressGestureRecognizer) {
    if longPress.state == .Began {
        presentAlertController()
    }
}

您只會收到一個帶有state .Began呼叫，因此您不會在警報已經呈現時再次嘗試呈現。